Spectrophotometric Study of Solution Equilibria between Ammonia and Copper(II) and Nickel(II) Chelates of Aminopolycarboxylic Acids

Abstract

Abstract The addition of ammonia produces a remarkable change in the visible absorption spectra of copper(II)- and nickel(II)-aminopolycarboxylate chelates. This can be ascribed to the formation of a mixed ligand chelate involving ammonia and the aminopolycarboxylate anion. On the basis of the change in the absorbance of copper(II)- and nickel(II)-aminopolycarboxylate chelates, the solution equilibria between ammonia and these aminopolycarboxylate chelates were investigated. Copper(II) and nickel(II) chelates of ethylenediaminetetraacetic acid (EDTA), N-(2-hydroxyethyl)-ethylenediamine-N,N′,N′-triacetic acid (EDTA-OH), ethylenediaminetetrapropionic acid (EDTP), cyclohexanediaminetetraacetic acid (CyDTA), and diethylenetriaminepentaacetic acid (DTPA) were found to form mixed ligand chelates with a composition of M(NH3)Z2−n. From the intercept of the linear relation between log(AY−A)⁄(A−AM) and log[NH3]f, the equilibrium constant, KNH3, defined as KNH3=[M(NH3)Z2−n]⁄[MZ2−n]·[NH3]f, was determined.